1. Field of the Invention
The present invention relates to a substrate for a magnetic disk suitable for high density recording and a process for its production.
2. Discussion of Background
Among various recording systems, the magnetic recording system is superior in the stability and the readiness for recording and reproduction and has been widely used. In recent years, however, there has been a strong demand for improvement of the recording density.
To meet the demand, .gamma.-Fe.sub.2 O.sub.3 having a coercive force at a level of 300 Oe and a high density recording material having a coercive force at a level of 600 Oe have been developed as magnetic recording media. Further, a thin film of Co-Ni alloy having a coercive force at a level of 1000 Oe has also been developed, whereby the linear recording density has reached to a level of 60 KBPI. Furthermore, a perpendicular magnetic recording system has been proposed, and it has been reported that a metallic thin film medium using a Co-Cr alloy provides a linear recording density of 300 KBPI.
Media using .gamma.-Fe.sub.2 O.sub.3 particles are widely practically used without problem with respect to the mechanical and chemical durability. However, metallic thin film media have problems with respect to the mechanical durability, etc., and they are not yet so commonly used.
Namely, a metallic thin film medium having a very smooth surface is likely to lead to sticking when brought in contact with a magnetic head. Further, a liquid lubricant applied to the medium is easily removed by the contact with the magnetic head, whereby the friction coefficient increases, thus leading to head crush.
In order to avoid such problems, a mechanical texture method has been attempted in which scratch marks are mechanically imparted to the surface of the substrate by means of e.g. sand paper. However, it is very difficult to impart such scratch marks while controlling not to increase bit errors and not to cause the sticking to the magnetic head. Further, in the mechanically scratched texture, fine burrs exist on the surface, and they tend to peel off upon collision with the magnetic head and thus lead to head crush.